The present invention relates to watercraft, and more particularly to a watercraft outdrive that can move a propeller and its shaft relative to a watercraft bottom while the watercraft is under power.
There is a variety of watercraft used in different activities. Some watercraft is used for commercial purposes, while others are used for recreation and/or competition. Many watercraft or boats are constructed to include an inboard motor. In such a construction, the engine of the boat is located inside the hull of the boat, while an outdrive projects rearward from the stern of the boat. The outdrive typically includes a transmission that transfers rotational forces from the engine to a propeller shaft and an associated propeller. Upon rotation, the propeller produces thrust to propel the boat through water.
Conventional outdrives of inboard watercraft typically are constructed so that the outdrive can tilt about a pivot point to tilt the propeller upward or tilt the propeller downward. Upon such tilting, however, the angle of the propeller and the associated thrust changes significantly. For example, when an outdrive is tilted upward, the tilted angle of the propeller makes maneuvering the boat more difficult because the thrust is projected upward toward the water surface instead of being projected rearward, behind the boat.
Even with such tilt features, an issue with conventional outdrives of inboard watercraft is that the vertical displacement of the propeller shaft and propeller is generally fixed and immovable relative to the bottom of the watercraft. With this fixed relationship relative to the bottom of the watercraft, conventional outdrives fail to effectively provide vertical adjustment of the propeller shaft and propeller, and thus the thrust point.
The fixed relationship of the propeller shaft relative to the bottom of the boat also presents challenges to boat builders. To mount a standard drive at the surface of water, the builder will mount the engine higher within the hull of the boat. This in turn raises the center of gravity of the boat, and in some cases, makes it unstable. Raising the center of gravity also can impair the boat's handling characteristics. This can create issues, particularly when the boat turns at high-speed.
With a given height of the engine above the bottom of the boat, boat builders also struggle to identify the ideal propeller shaft location relative to the bottom of the boat when setting it in that fixed, permanent position. Usually, the builder uses trial and error techniques to place the propeller shaft at a particular location. Some boat builders and consumers will attempt to change the location of the propeller shaft relative to the bottom of the boat. For example, a consumer might purchase an outdrive lower unit that differs from the OEM lower unit offered at a standard height. These outdrive lower units typically enable the user to adjust the propeller shaft location in one inch increments.
An issue with modifying the outdrive to replace one lower unit for another is that this modification must be done by disassembling the outdrive and its components out of the water. This can be time-consuming and expensive. Users also can utilize spacer plates that are placed between upper and lower units of the outdrive. Again, however, the final set up of the spacer plate and/or different lower unit is fixed and cannot be changed without disassembling the lower unit to add or subtract a spacer plate or to replace the lower unit altogether with a different sized lower unit.
Another complicating factor in finding the ideal propeller shaft location is that the configuration and loading of the watercraft can change what that ideal propeller shaft location should be. For example, when a watercraft is loaded with gear and occupants on board, this can alter the ideal propeller shaft location. Full or empty fuel tanks also can change the location.
Further, with a fixed and immovable propeller shaft location, conventional outdrives can limit performance, particularly in race boats. Race boats typically run the propeller shaft at the surface of the water when the boat is under power to maximize speed. When the race boat turns around an obstacle, such as a buoy, at speed, less skeg of the outdrive is in the water. With less skeg in the water, the boat is more prone to skim the surface of the water and potentially spin out. In some cases, this can create a dangerous situation for the racers as well as observers.
Surface drive boats with a fixed and immovable propeller shaft location also are difficult to maneuver around a dock or other obstacle where a reverse direction is helpful. For example, surface drive propellers, when in reverse, thrust water against the stern, and in particular the transom of the boat. This helps very little to propel the boat rearward because this thrust is wasted.
Accordingly, there remains room for improvement in the field of outdrives for watercraft with inboard motors.